According to an AFP reporter who witnessed the incident, Kosciusko, known in France as NKM, was approached by a man as she handed out campaign leaflets at a market in the fifth arrondissement of Paris, where she is hoping to be elected MP.
The man, aged in his 50s, called the former minister a dirty 'bobo', a term that comes from a blend of bourgeois and bohemian and is often used in a derogatory way to describe Paris's wealthy middle class young professionals.
He also shouted "It's your fault we have Anne Hidalgo as mayor" referring to the fact NKM lost out to Hidalgo in the 2014 mayoral race. He also yelled "go back to l'Essonne", the department near Paris for which she is currently an MP.
Some reports say he then tried to hit her while BFM TV said she was violently pushed by the man.
Others suggested she fell when trying to protect herself when he threw her leaflets in her face.
She lost consciousness for several minutes after apparently hitting her head as she fell.
The shaved headed man, dressed in a shirt and chinos, ran off to the nearest Metro station.
According to reports a memebr of NKM's team followed him on the Metro and later confronted him before being attacked.
He was not known to the candidate's campaign team, Le Parisien newspaper reports.
NKM, who lost out to François Fillon in last year's right-wing presidential primary, was reportedly treated at the scene by paramedics before being taken to hospital.
She has received messages of solidarity from many disgusted French politicians from all sides including Socialist Paris Mayor Anne Hidalgo, who strongly condemned the man's actions calling it a "cowardly and intolerable" act.
Former Socialist PM Manuel Valls also expressed his solidarity to NKM saying "nothing could justify this intolerable act".
Toute ma solidarité avec @nk_m.à qui j'adresse soutien et affection.Je condamne cette agression intolérable que rien ne pourra justifier— Manuel Valls (@manuelvalls) June 15, 2017
Fellow conservative, and another beaten presidential candidate, Alain Juppé sent NKM his best wishes and commended her courage.
She was also visited in hospital by Prime Minister Edouard Philippe.
"I condemn this intolerable act of violence," said the PM.
NKM, 44, is campaigning ahead of the second round of France's parliamentary election this Sunday.
The former minister and spokeswoman under ex-president Nicolas Sarkozy faces a battle to win a seat in her central Paris constituency against Gilles Le Gendre from the Republic on the Move party of President Emmanuel Macron.
Le Gendre anonced on Thursday that he was suspending his campaign in light of what had happened to his opponent.